Lithographic apparatus and device manufacturing method

ABSTRACT

A lithography apparatus includes a projection system configured to project a radiation beam onto a substrate, a detector configured to inspect the substrate, and a substrate table configured to support the substrate and move the substrate relative to the projection system and the detector. The detector is arranged to inspect a portion of the substrate while the substrate is moved and before the portion is exposed to the radiation beam.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lithographic apparatus and a devicemanufacturing method.

2. Related Art

A lithographic apparatus is a machine that applies a desired patternonto a target portion of a substrate. Lithographic apparatus can beused, for example, in the manufacture of integrated circuits (ICs), flatpanel displays and other devices involving fine structures. In aconventional lithographic apparatus, a patterning means, which isalternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern corresponding to an individual layer of theIC (or other device), and this pattern can be imaged onto a targetportion (e.g., comprising part of one or several dies) on a substrate(e.g., a silicon wafer or glass plate) that has a layer ofradiation-sensitive material (resist). Instead of a mask, the patterningmeans may comprise an array of individually controllable elements thatgenerate the circuit pattern on an impinging light beam.

In general, a single substrate will contain a network of adjacent targetportions that are successively exposed. Lithographic apparatus includesteppers, in which each target portion is irradiated by exposing anentire pattern onto the target portion in one pass, and scanners, inwhich each target portion is irradiated by scanning the pattern throughthe projection beam in a given direction (the “scanning”-direction),while synchronously scanning the substrate parallel or anti-parallel tothis direction.

In order to manufacture devices using lithographic techniques, it istypically necessary to form the device from multiple layers. Whenproducing such a device from multiple layers, as each layer is createdit is aligned with the previous layers. It has therefore been known toprovide alignment marks on a substrate. Before each layer is exposed onthe substrate, it is transported to an alignment measuring area, wherethe alignment marks are detected, allowing a precise determination ofthe position of the substrate relative to the alignment sensors. Bymoving the substrate in a controlled manner to the exposure position, apositional correction can be applied to accurately produce thesubsequent layer in the correct position on the substrate. Such a systemcan be used to ensure that the overlay errors are small in comparison tothe critical feature size.

However, as the critical feature size continues to diminish, furtherimprovements in the overlay accuracy are required. Furthermore, as thealignment requirements increase, the time taken to locate and inspectthe alignment marks increases, reducing the throughput of the apparatus.

Therefore, what is needed is a method and an apparatus in which theoverlay accuracy can be improved without significant loss of throughputof the apparatus.

BRIEF SUMMARY OF THE INVENTION

One embodiment of the present invention provides a lithographicapparatus. The lithography apparatus includes a projection systemconfigured to project a radiation beam onto a substrate, a detectorconfigured to inspect the substrate, and a substrate table configured tosupport the substrate and move the substrate relative to the projectionsystem and the detector. The detector is arranged to inspect a portionof the substrate while the substrate is moved and before the portion isexposed to the radiation beam.

Another embodiment of the present invention provides a devicemanufacturing method. The method includes moving a substrate relative toa projection system and a detector, inspecting a portion of thesubstrate using the detector, exposing the portion of the substrateusing the projection system while the exposure conditions are adjustedaccording to the inspection.

It will be appreciated that combinations of the configurations discussedabove may also be used.

Further embodiments, features, and advantages of the present invention,as well as the structure and operation of the various embodiments of thepresent invention are described in detail below with reference toaccompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate various embodiments of the presentinvention and, together with the description, further serve to explainthe principles of the invention and to enable a person skilled in thepertinent art to make and use the invention.

FIG. 1 depicts a lithographic apparatus.

FIGS. 2 a, 2 b and 2 c depict a substrate at three time instances as alayer on the substrate is being exposed.

FIG. 3 depicts an arrangement of an exposure unit used in thelithographic apparatus.

FIG. 4 depicts a part of an exposure unit as shown in FIG. 3.

FIG. 5 depicts the exposure field produced by an exposure system asshown in FIG. 3.

FIG. 6 depicts an example of an arrangement of repeating units offeatures formed on a substrate.

FIG. 7 depicts an arrangement of a detector unit used in a lithographicapparatus.

In the Figures, corresponding reference symbols indicate correspondingparts

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Terminology

The term “array of individually controllable elements” as here employedshould be broadly interpreted as referring to any means that can be usedto endow an incoming radiation beam with a patterned cross-section, sothat a desired pattern can be created in a target portion of thesubstrate; the terms “light valve” and “Spatial Light Modulator” (SLM)can also be used in this context. Examples of such patterning meansinclude, but are not limited to, a programmable mirror array and aprogrammable liquid crystal device (LCD) array.

A programmable mirror array may comprise a matrix-addressable surfacehaving a viscoelastic control layer and a reflective surface. The basicprinciple behind such an apparatus is that addressed areas of thereflective surface reflect incident light as diffracted light, whereasunaddressed areas reflect incident light as undiffracted light. Using anappropriate spatial filter, the undiffracted light can be filtered outof the reflected beam, leaving only the diffracted light to reach thesubstrate. In this manner, the beam becomes patterned according to theaddressing pattern of the matrix-addressable surface.

It will be appreciated that, as an alternative, the filter may filterout the diffracted light, leaving the undiffracted light to reach thesubstrate.

An array of diffractive optical MEMS devices can also be used in acorresponding manner. Each diffractive optical MEMS device is comprisedof a plurality of reflective ribbons that can be deformed relative toone another to form a grating that reflects incident light as diffractedlight.

A further alternative embodiment of a programmable mirror array employsa matrix arrangement of tiny mirrors, each of which can be individuallytilted about an axis by applying a suitable localized electric field, orby employing piezoelectric actuation means. Once again, the mirrors arematrix-addressable, such that addressed mirrors will reflect an incomingradiation beam in a different direction to unaddressed mirrors. In thismanner, the reflected beam is patterned according to the addressingpattern of the matrix-addressable mirrors.

The matrix addressing can be performed using suitable electronic means.In the examples described above, the array of individually controllableelements can comprise one or more programmable mirror arrays. Moreinformation on mirror arrays can be found, for example, from U.S. Pat.Nos. 5,296,891 and 5,523,193, and PCT patent applications WO 98/38597and WO 98/33096, which are incorporated herein by reference.

An example programmable LCD array is shown in U.S. Pat. No. 5,229,872,which is incorporated herein by reference.

It should be appreciated that where pre-biasing of features, opticalproximity correction features, phase variation techniques, and multipleexposure techniques are used, for example, the pattern “displayed” onthe array of individually controllable elements may differ substantiallyfrom the pattern eventually transferred to a layer of or on thesubstrate. Similarly, the pattern eventually generated on the substratemay not correspond to the pattern formed at any one instant on the arrayof individually controllable elements. This may be the case in anarrangement in which the eventual pattern formed on each part of thesubstrate is built up over a given period of time or a given number ofexposures, during which the pattern on the array of individuallycontrollable elements and/or the relative position of the substratechanges.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat panel displays, thin-film magnetic heads, etc. The skilled artisanwill appreciate that, in the context of such alternative applications,any use of the terms “wafer” or “die” herein may be considered assynonymous with the more general terms “substrate” or “target portion,”respectively.

The substrate referred to herein may be processed, before or afterexposure, in for example a track (a tool that typically applies a layerof resist to a substrate and develops the exposed resist) or a metrologyor inspection tool. Where applicable, the disclosure herein may beapplied to such and other substrate processing tools. Further, thesubstrate may be processed more than once, for example in order tocreate a multi-layer IC, so that the term substrate used herein may alsorefer to a substrate that already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including, but not necessarily limited to,ultraviolet (UV) radiation (e.g. having a wavelength of 408, 355, 365,248, 193, 157 or 126 nm) and extreme ultra-violet (EUV) radiation (e.g.having a wavelength in the range of 5-20 nm), as well as particle beams,such as ion beams or electron beams.

The term “projection system” used herein should be broadly interpretedas encompassing various types of projection systems, includingrefractive optical systems, reflective optical systems, and catadioptricoptical systems, as appropriate for example for the exposure radiationbeing used, or for other factors such as the use of an immersion fluidor the use of a vacuum. Any use of the term “lens” herein may beconsidered as synonymous with the more general term “projection system.”

The illumination system may also encompass various types of opticalcomponents, including refractive, reflective, and catadioptric opticalcomponents for directing, shaping, or controlling the projection beam ofradiation, and such components may also be referred to below,collectively or singularly, as a “lens”.

The lithographic apparatus may be of a type having two (dual stage) ormore substrate tables. In such “multiple stage” machines the additionaltables may be used in parallel, or preparatory steps may be carried outon one or more tables while one or more other tables are being used forexposure.

The lithographic apparatus may also be of a type wherein the substrateis immersed in a liquid having a relatively high refractive index, e.g.water, so as to fill a space between the final element of the projectionsystem and the substrate. Immersion liquids may also be applied to otherspaces in the lithographic apparatus, for example, between the array ofindividually controllable elements and the first element of theprojection system. Immersion techniques are well known in the art forincreasing the numerical aperture of projection systems.

Exemplary Environment

FIG. 1 schematically depicts a lithographic projection apparatus,according to one embodiment of the invention. The apparatus comprises anillumination system (illuminator) IL, an array of individuallycontrollable elements PPM, a substrate table WT for supporting asubstrate W, and a projection system (“lens”) PL.

Illumination system (illuminator) IL provides a projection beam PB ofradiation (e.g. UV radiation).

The array of individually controllable elements PPM (e.g., aprogrammable mirror array) patterns the projection beam. In one example,the position of the array of individually controllable elements will befixed relative to projection system PL. In another example, it mayinstead be connected to a positioning means for accurately positioningit with respect to projection system PL.

As discussed above, the substrate table WT (e.g., a wafer table)supports the substrate W (e.g. a resist-coated wafer). The substratetable WT is also connected to a positioning means PW for accuratelypositioning the substrate with respect to projection system PL.

The projection system (“lens”) PL images a pattern imparted to theprojection beam PB by the array of individually controllable elementsPPM onto a target portion C (e.g., comprising one or more dies) of thesubstrate W. In one example, the projection system PL may image thearray of individually controllable elements PPM onto the substrate W. Inanther example, the projection system PL may image secondary sources,for which the elements of the array of individually controllableelements PPM act as shutters. The projection system PL may also comprisean array of focusing elements, such as a micro lens array (known as anMLA) or a Fresnel lens array. This can be done, for example, to form thesecondary sources and to image microspots onto the substrate.

In the embodiment shown, the apparatus is of a reflective type (i.e.,has a reflective array of individually controllable elements). However,in general, it may also be of a transmissive type, e.g., with atransmissive array of individually controllable elements.

The illuminator IL receives a beam of radiation from a radiation sourceSO. In one example, the source SO and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BD. Inthis case the beam delivery system BD includes, but is not limited to,suitable directing mirrors and/or a beam expander. In other examples thesource SO may be integral part of the apparatus, for example when thesource is a mercury lamp. In this example, the source SO and theilluminator IL, together with the beam delivery system BD, if required,may be referred to as a radiation system.

The illuminator IL may comprise adjusting means AM for adjusting theangular intensity distribution of the beam. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator IL can be adjusted. In some examples the illuminator ILcomprises various other components, such as an integrator IN and acondenser CO. The illuminator IL provides a conditioned beam ofradiation, referred to as the projection beam PB, having a desireduniformity and intensity distribution in its cross-section.

The beam PB subsequently interacts with the array of individuallycontrollable elements PPM. Having been reflected by the array ofindividually controllable elements PPM, the beam PB passes through theprojection system PL, which focuses the beam PB onto a target portion Cof the substrate W.

In one example, with the aid of a positioning means PW, and possibly aninterferometric measuring means IF, the substrate table WT can be movedaccurately, e.g., so as to position different target portions C in thepath of the beam PB.

In one example, a positioning means PW for the array of individuallycontrollable elements PPM can be used to accurately correct the positionof the array of individually controllable elements PPM with respect tothe path of the beam PB, e.g. during a scan.

In one example, movement of the substrate table WT is realized with theaid of a long-stroke module (course positioning) and a short-strokemodule (fine positioning), which are not explicitly depicted in FIG. 1.A similar system may also be used to position the array of individuallycontrollable elements PPM.

It will be appreciated that the projection beam PB mayalternatively/additionally be moveable while the substrate table WTand/or the array of individually controllable elements PPM may have afixed position to provide the required relative movement.

As a further alternative, that may be especially applicable in themanufacture of flat panel displays, the position of the substrate tableWT and the projection system PL may be fixed and the substrate W may bearranged to be moved relative to the substrate table WT. For example,the substrate table WT may be provided with a system for scanning thesubstrate W across it at a substantially constant velocity.

Although the lithography apparatus according to the invention is hereindescribed as being for exposing a resist on a substrate, it will beappreciated that the invention is not limited to this use and theapparatus may be used to project a patterned projection beam for use inresistless lithography.

The depicted apparatus can be used in four preferred modes: a step mode,a scan mode, a pulse mode, and a continuous scan mode.

In a step mode, the array of individually controllable elements PPMimparts an entire pattern to the projection beam PB, which is projectedonto a target portion C in one pass (i.e., a single static exposure).The substrate table WT is then shifted in the X and/or Y direction, sothat a different target portion C can be exposed. In step mode, themaximum size of the exposure field limits the size of the target portionC imaged in a single static exposure.

In Scan mode, the array of individually controllable elements PPM ismovable in a given direction (e.g., a “scan direction” or a Y direction)with a speed v, so that the projection beam PB is caused to scan overthe array of individually controllable elements PPM. Concurrently, thesubstrate table WT is substantially simultaneously moved in the same oropposite direction at a speed V=Mv, in which M is the magnification ofthe lens PL. In scan mode, the maximum size of the exposure field limitsthe width (in the non-scanning direction) of the target portion C in asingle dynamic exposure, whereas the length of the scanning motiondetermines the height (in the scanning direction) of the target portionC.

In Pulse mode, the array of individually controllable elements PPM iskept essentially stationary and the entire pattern is projected onto atarget portion C of the substrate W using a pulsed radiation system. Thesubstrate table WT is moved with an essentially constant speed, suchthat the projection beam PB is caused to scan a line across thesubstrate W. The pattern on the array of individually controllableelements PPM is updated as required between pulses of the radiationsystem. The pulses are timed such that successive target portions C areexposed at the required locations on the substrate W. Consequently, theprojection beam PB scans across the substrate W to expose the completepattern for a strip of the substrate W. The process is repeated untilthe complete substrate W has been exposed line by line.

Continuous scan mode is essentially the same as pulse mode except that asubstantially constant radiation source is used and the pattern on thearray of individually controllable elements PM is updated as theprojection beam PB scans across the substrate W and exposes it.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Exemplary Projection Optical Systems

FIGS. 2 a, 2 b and 2 c illustrate three states of a section of theapparatus, according to one embodiment of the present invention. In thesection, an exposure and alignment module 15 is provided in a fixedlocation and a substrate 10 is scanned beneath exposure and alignmentmodule 15. FIG. 2 a depicts a first state, which is immediately beforesubstrate 10 reaches exposure and alignment module 15. FIG. 2 b depictsa second state, which is when substrate 10 begins to scan beneathexposure and alignment module 15. FIG. 2 c depicts a third state, whichis when substrate 10 continues to scan beneath exposure and alignmentmodule 15.

In one example, exposure and alignment module 15 is comprised of adetector unit 16 and an exposure unit 17. Detector unit 16 and exposureunit 17 are connected by means of a reference frame 18, which ensuresthat the relative position of exposure unit 17 to detector unit 16 isfixed. Reference frame 18 may be formed from a material having very lowthermal expansion to ensure that the relative positions are stable. Therelative position can then be accurately determined by priorcalibration.

As substrate 10 is scanned beneath exposure and alignment module 15,detector unit 16 inspects alignment marks (not shown) on substrate 10.The information from inspecting the alignment marks is used toaccurately determine the position of substrate 10 in the scan direction,in the transverse direction (i.e., within the plane of substrate 10 andperpendicular to the scan direction), and perpendicular to substrate 10.Furthermore, the alignment marks may be used to ascertain theorientation of substrate 10 in all three degrees of rotational freedom.Detector unit 16 also inspects the alignment marks to determine theextent of any thermal expansion/contraction of substrate 10.

As substrate 10 scans beneath exposure and alignment unit 15, each partof substrate 10 passes first under detector unit 16 and then underexposure unit 17. Consequently, the linear position, orientation, andexpansion information, determined by detector unit 16, for each portionof substrate 10 can be transferred to exposure unit 17 so that theexposure conditions for that portion of substrate 10 can be optimizedwhen it is exposed as it passes underneath exposure unit 17.

In particular, the position of the pattern projected onto the portion ofsubstrate 10 can be adjusted for errors in the position of the portionof substrate 10 in the scan and transverse directions. The best focusimage plane can be adjusted for errors in the position of that portionof substrate 10 in the direction perpendicular to the plane of substrate10. Magnification corrections can be made to correct for any thermalexpansion/contraction of that portion of substrate 10.

In an example when the apparatus is used for the manufacture of flatpanel displays, detector unit 16 may be positioned 30 cm in advance ofexposure unit 17 (from the point of view of the advancing substrate).The scan speed of substrate 10 relative to detector unit 16 and exposureunit 17 may be 50 mm per second. Consequently the apparatus has 6seconds in between inspecting a portion of substrate 10 using detectorunit 16 and illuminating the same portion with exposure unit 17. This issufficient time for the data from detector unit 16 to be used to adjustthe exposure settings, as required, in the exposure unit.

The alignment marks on each portion of substrate 10 are inspected,allowing continuous corrections to be made. Consequently, overlay errorscan be reduced even when there is local deformation of substrate 10.

A time difference between inspecting the alignment marks and substrate10 and exposing the pattern on that part of substrate 10 is only limitedby the separation of detector unit 16 and exposure unit 17 and thescanning speed of substrate 10. This is in contrast to presently knownapparatus in which the substrate is first scanned in its entirety foralignment marks and then scanned in its entirety to expose the pattern.This results in a large time difference between a given portion of thesubstrate being inspected for alignment marks and that portion beingexposed. During this time, additional deformations may be introducedwhich will result in overlay errors. For example, as the substrate isexposed, the radiation projected onto the substrate increases itstemperature. This temperature increase results in a thermal expansion ofthe substrate. In known systems, this thermal expansion during exposurecannot be accounted for by inspecting alignment marks in a process thatis separate from the exposure. In the present invention, however, thisexpansion is accounted for since the alignment marks are inspected asthe exposure takes place. It is especially important for flat-paneldisplay lithography which may be used to image soda-lime glass plates upto two meters long. For such a plate, the expansion would beapproximately 8 μm per 1° C. temperature change. Therefore, to provide arequired overlay accuracy of 0.35 μm without inspecting alignment marksduring exposure, the temperature of substrate 10 would need to becontrolled to ±0.05° C. over the entire plate. This would requirecomplicated thermal control.

Furthermore, since the present invention does not require a separateprocess for inspecting the alignment marks on substrate 10, theprocessing time for each substrate is greatly reduced.

In various examples, the alignment marks on substrate 10 may be:alignment gratings parallel to both the scan direction and thetransverse direction, chevron alignment marks, or image recognition viaTV imaging. In another example, a sequence of alignment marks may bearranged in one or more rows parallel to the direction in whichsubstrate 10 is scanned relative to detector unit 16 and distributedover the length of substrate 10. In one example, at least two such rowsof alignment marks are provided on the substrate. In each case, knowndetection optic systems, appropriate for the alignment marks used, areprovided in detector unit 16.

In one example, dedicated alignment marks are not provided on substrate10. Instead, detector unit 16 is provided with one or more sensors (notshown) that can detect the pattern of the features that have been formedon substrate 10 in previous processing steps. Such sensors may becameras connected to controllers that run pattern recognitionalgorithms. This arrangement can be beneficial because a dedicatedalignment mark represents a portion of substrate 10 that cannot be usedfor a feature of the device being formed on substrate 10. Therefore, byusing features of the formed device itself, a greater portion ofsubstrate 10 can be used for functioning components of the formeddevice.

For example, this arrangement is used in the formation of flat paneldisplays. An alignment mark may be approximately the same size as apixel of the display being formed. Therefore, if an alignment mark wererequired within the display, this would result in the absence of a pixelat that location in the formed device, which would clearly beunacceptable.

The use of features formed in a previous layer is also used foralignment. When a new layer is being formed on a device on a substrate10, it is essential to ensure that it is correctly overlaid with theprevious layers that have been formed on the device. By directlymeasuring the position of the features of the earlier layers formed onsubstrate 10, one can ensure that the next layer is correctly overlaid.

If, as described, detector unit 16 inspects functional features of thedevice being formed instead of dedicated alignment marks, it may benecessary around the edges of the device being formed to include dummyfeatures (i.e., those that appear similar to the functional features) inorder to ensure that the alignment is correct when forming thefunctional features at the edge of the device.

FIG. 6 schematically represents a portion of a feature pattern that maybe formed on a substrate during the manufacture of a flat panel display,according to one embodiment of the present invention. An overall patternis made up of a plurality of repeating units 40, comprising controllines 41, a thin film transistor 42, and a pixel 43.

In one example, an image recognition system may be used to identifyrepeating units 40 and accurately measure the position of the features.For example, a self-learning image recognition system may be used. Asnoted, the patterns are highly repeatable. Therefore, the imagerecognition detector may be used for the fine measurements of theposition of the features on the substrate and a separate system may beused for coarse position measurement because there may be nodistinguishable difference between the repeated units on different partsof the substrate.

In one example, a ruler may be provided on the substrate, namely aseries of marks to indicate the position along the length of thesubstrate. The ruler may, for example, only be provided along the edgeof the substrate because it is only being used for the coarsemeasurement of the position of the features of the device formed on thesubstrate. In other words, the ruler need not be formed at a position onthe substrate where it would be desirable to form features of the deviceto be formed on the substrate.

Alternatively, or additionally, the image recognition sensor may be ableto perform the coarse position measurement by storing information as thesubstrate scans relative to the detector unit. For example, the detectorunit may count the number of repeating units 40 of the pattern ofpreceding layers formed on the substrate that have already scanned pastthe detector unit. This count data can therefore be used to determinewhich of the repeating units is subsequently identified by the patternrecognition detector.

With reference back to FIGS. 2 a, 2 b, and 2 c, a position of thepattern that is projected onto substrate 10 may be moved by severalmeans. Firstly, the position of substrate 10 may be corrected as itscans beneath exposure and alignment unit 15.

In one example, the substrate table may be mounted on a long-strokemodule (not shown) that provides the scanning motion, while ashort-stroke module (not shown) is mounted between the long-strokemodule and the substrate table WT to provide the corrective movement.

In another example, exposure and alignment unit 15 or, at least, theexposure unit 17 (or a part thereof) may be mounted on an actuator (notshown) to provide corrective movements in order to project the patternonto the correct portion of substrate 10.

In another example, the pattern formed on the array of individuallycontrollable elements PPM is moved electronically. For example, the dataprovided to the array of individually controllable elements PPM isadjusted, such that the pattern appears shifted on the array ofindividually controllable elements PPM. In this case, the position ofthe pattern projected onto substrate 10 in a direction parallel to thescanning direction can also be adjusted by controlling the timing of theexposure of the pattern as substrate 10 is scanned beneath exposure unit17 or adjusting the timing of a pattern being set on the array ofindividually controllable elements PPM if, for example, the apparatus isused in a continuous scan mode. Of course, a combination of theabove-described techniques may also be used.

Exemplary Exposure Unit

FIG. 3 depicts an exposure unit 17, according to one embodiment of thepresent invention. Exposure unit 17 is comprised of a plurality of lightengines 21 that are each capable of producing a patterned beam ofradiation and projecting it onto substrate 10. Light engines 21 arearranged in first and second arrays 22, 23 perpendicular to the scandirection of substrate 10.

FIG. 4 shows a light engine 21, according to one embodiment of thepresent invention. Each light engine 21 is comprised of an array ofindividually controllable elements 25, projection optics 26, and amicro-lens array 27 (MLA). In various examples, two or more lightengines 21 may share a common radiation source or each may be providedwith an independent radiation source. It will also be appreciated thatthe array of individually controllable elements 25 may be wholly imagedonto the substrate 10 without using an MLA.

FIG. 5 shows features formed on substrate 10, according to oneembodiment of the present invention. In this embodiment, arrays 22, 23of light engines 21 produce corresponding formed feature arrays 32, 33of pattern images 31 on substrate 10. In each array 22, 23 of lightengines 21, space is provided between each light engine 21. This spacemay be used to provide ancillary services for light engines 21, such ascooling, or to provide space for radiation sources. Consequently, thereare gaps in arrays 32, 33 of patterned images 31 projected ontosubstrate 10. Arrays 22, 23 of light engines 21 are arranged such thatsecond array 32 of patterned images 31 projected onto substrate 10 bysecond array of light engines 22 coincide with the gaps in the firstarray 33 of patterned images projected onto the substrate by first array23 of light engines 21 after substrate 10 has moved a given distance.Consequently, a complete strip of substrate 10 across the transversedirection can be exposed notwithstanding the gap between light engines21.

In FIGS. 3 and 5, there are two arrays of light engines 21. It will beappreciated, however, that additional arrays can be provided in exposureunit 17. This can be, for example, to allow for larger gaps betweenlight engines 21 or to allow each part of substrate 10 to receive morethan one exposure within a single scan.

In one example, each of the adjustments that are made to pattern 31projected onto substrate 10 in response to information from detectorunit 16 can be made independently by each of light engines 21. This maybe effected by providing individual actuators to control the position ofeach light engine 21, by providing magnification control and best focusimage plane control in the projection optics 26 and/or the micro lensarrays of each light engine 21 and/or by providing separate data controlfor each light engines 21, so that electronic corrections can be appliedindependently. By this means it is possible to compensate for localdistortions and deformations across substrate 10. It may, however, bedesirable to also provide global compensation means (i.e., compensationmeans that affect the pattern produced by all light engines 21) tocompensate for, for example, positional errors of substrate 10 as awhole.

Where light engines 21 are not mounted on separate actuators, themicro-lens arrays 27 of all light engines 21 may be mounted on a singlereference frame that, in one example, has a very low thermal expansion.However, if required, the position of each micro-lens array 27 relativeto the reference frame may be adjustable. Similarly, the array ofindividually controllable elements PPM of all light engines 21 may bemounted on a separate reference frame and the position of each relativeto the reference frame may be adjustable. Consequently, the relativepositions of the patterns produced by light engines 21 can be measuredand calibrated.

The magnification of each light engine 21 can be adjusted by changingthe position of the array of individually controllable elements PPM tocompensate for any expansion/contraction of substrate 10, or by anyother suitable optical method. Alternatively or additionally, themagnification of the pattern projected onto substrate 10 can be adjustedby electronically changing the pattern applied to the array ofindividually controllable elements PPM. As before, this may be performedindependently for each light engine 21 and/or globally for all lightengines 21. For example, this can be done by adjusting the position ofthe reference frame on which all of the arrays of individuallycontrollable elements are mounted. In one example, the magnificationcontrol range is about ±15 ppm.

In a variant of the above-described embodiment, detector unit 16 andexposure unit 17 may not be rigidly connected to one another or may beconnected by a frame that is subject to thermal expansion/contraction.In this case, a position sensor must be provided to monitor the positionof exposure unit 17 relative to detection unit 16. Thus the relativeposition remains known, even if it is not fixed.

Exemplary Detector Unit

FIG. 7 shows detector unit 16, according to one embodiment of thepresent invention. In this embodiment, detector unit 16 comprises aplurality of sensors 16 a,16 b such that the alignment marks and/orfeatures of previously formed layers on substrate 10 can be inspectedacross the full width of substrate 10. Consequently, variations acrossthe width of substrate 10 in the deformation of substrate 10 and/or thealignment of features already formed on substrate 10 can be taken intoaccount when setting the exposure conditions in exposure unit 17.

In this embodiment, sensors 16 a,16 b in detector unit 16 may bearranged in a manner corresponding to that of the light engines inexposure unit 17. For example, sensors 16 a,16 b may be arranged in afirst array of sensors 16 a and second array of sensors 16 b, each arraycomprising a set of spaced apart sensors. Therefore, although the fullwidth of substrate 10 is inspected, clearance can be provided aroundeach sensor 16 a,16 b for control lines, services, etc.

It will be appreciated that in an arrangement as described above, eachsensor 16 a,16 b may be arranged such that it is associated with a givenlight engine 21, namely each portion of the substrate that is inspectedby a given sensor is subsequently exposed using the associated lightengine. It will also be appreciated that this arrangement need not belimited to two rows of sensors 16 a,16 b as shown in FIG. 7 but may beconfigured with any number of rows, as convenient. In addition, detectorunit 16 may be arranged such that it does not inspect each part ofsubstrate 10. For example, a row of sensors may be arranged across thewidth of detection unit 16, but set apart from one another. In thiscase, the sensors are arranged to measure the position and/ororientation of the substrate and/or the features formed on the substrateat a plurality of locations that are set apart from one another. Theexposure condition can therefore be set for these areas on the substratedirectly from the measurements from the sensors. For the areas inbetween, which have not been inspected by sensors, the exposureconditions may be set by interpolating the data from two or more sensorsthat have inspected the surrounding portions of the substrate.

It is further to be appreciated that although the invention has beenprimarily described above in relation to an apparatus that uses thepulse mode (described above), in which substrate 10 is moved at anessentially constant speed and the exposures are pulsed, it will beappreciated that the invention may equally be applied to apparatus thatoperates in a stepped mode (described above) and apparatus that operatesin a scan mode (described above).

Furthermore, although the invention refers to the use of an array ofindividually controllable elements PPM for patterning radiation beam PB,it will be appreciated that the invention may be equally applied toapparatus using a conventional fixed mask to pattern the projection beamPB. In this case, it may be used, for example, with an apparatusoperating in scan mode. The detector could be located between the maskand the substrate and arranged to precede the patterned projection beamas it scans across the substrate.

Finally, although the invention has been described in terms of substrate10 being moved below exposure and alignment unit 15, it will be readilyappreciated that the absolute positions described are not essential tothe invention, nor is it essential that a given part of the apparatus befixed. It is only necessary that substrate 10 move relative to exposureand alignment unit 15.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described. The description is not intended to limit theinvention.

What is claimed is:
 1. A lithography apparatus comprising: a projectionsystem comprising a plurality of projection optics arranged in adirection across a substrate, each of the projection optics forprojecting a radiation beam onto a substrate; a detector unit forinspecting the substrate comprising a plurality of detectors arranged inthe direction such that each detector in the plurality of detectors isaligned with an associated projection optic in the plurality ofprojection optics; and a substrate table configured to support thesubstrate and move the substrate relative to the projection system andthe detector unit; wherein each detector is arranged to inspect aportion of the substrate while the substrate is moved and before theportion is exposed to the radiation beam projected by the associatedprojection optic.
 2. The apparatus of claim 1, wherein the plurality ofdetectors are arranged to simultaneously inspect a plurality of portionsof the substrate across the full width of the substrate.
 3. Theapparatus of claim I, further comprising a controller for adjustingexposure conditions based on said inspecting.
 4. The apparatus of claim1, wherein the apparatus is configured to provide a patterned beam usingan array of individually controllable elements.
 5. The apparatus ofclaim 4, wherein the apparatus comprises a plurality of arrays ofindividually controllable elements.
 6. A device manufacturing methodcomprising: moving a substrate relative to a projection systemcomprising a plurality of projection optics arranged in a directionacross the substrate and a detector unit comprising a plurality ofdetectors arranged in the direction such that each detector in theplurality of detector is aligned with an associated projection optic inthe plurality of projection optics; inspecting a portion of thesubstrate using each of the detectors; and exposing the portion of thesubstrate using each of the associated projection optics while theexposure conditions are adjusted according to the inspection.
 7. Themethod of claim 6, wherein the inspecting and the exposing occurs whilemoving the substrate.
 8. The method of claim 6, wherein moving thesubstrate relative to the projection system and the detector unit occursbetween consecutive exposures.
 9. The method of claim 6, wherein movingthe substrate relative to the projection system and the detector unitoccurs during continuous exposure.
 10. The method of claim 6, whereinthe portion of the substrate being inspected subsequently becomes theportion of the substrate being exposed.
 11. The method of claim 6,wherein the exposure conditions are adjusted to optimize for overlayaccuracy.
 12. The method of claim 6, wherein the substrate moves at asubstantially constant velocity relative to the projection system andthe detector unit.
 13. The method of claim 6, wherein the position ofthe detectors relative to the projection system is substantially fixedand known.
 14. The method of claim 6, further comprising monitoring theposition of the detectors relative to the projection system duringexposure.
 15. The method of daub 6, wherein the portion of the substratecomprises the full width of the substrate.